CBM

Numerical simulation study on the influence of coal rock fracture morphology on seepage capacity

  • Leiting SHI ,
  • Qiming ZHAO ,
  • Zhenyu REN ,
  • Shijie ZHU ,
  • Shanshan ZHU
Expand
  • 1. State Key Laboratory of Oil and Gas Reservoir Geology and Development Engineering, Southwest Petroleum University, Chengdu, Sichuan 610500, China
    2. Chongqing Energy College, Chongqing 402260, China
    3. China United Coalbed Methane Corp. Ltd., Beijing 100016, China
    4. School of Petroleum Engineering, Chongqing University of Science & Technology, Chongqing 401331, China

Received date: 2023-03-31

  Online published: 2023-09-01

Abstract

The fracture network developed in coal rock serves as the primary channel for gas migration, significantly influencing the seepage capacity of coal reservoir. The geometric characteristics of fracture plays a crucial role on determining the flow characteristics of coal-bed methane. To study this, a two-dimensional fracture network model of coal rock was established using COMSOL Multiphysics simulation software, focusing on the coal samples of Baode block as the research subject. The effects of fracture length, density, opening degree and angle on production were investigated, providing valuable theoretical guidance for enhancing coal-bed methane production. The results indicate that fracture length, density, and opening degree have a positive correlation with the seepage capacity of coal rock, while the angle with the flow direction negatively impacts it. However, with the increase of length, density and opening degree, the improvement in flow rate slows down, and the effect of increasing single factor to improve coal-bed methane mining can be neglected, making it difficult to control the cost-benefit ratio. Among the factors influencing outlet, angle and density exert a more significant effect than length and opening degree. Considering the surface directional well plus the high pressure hydraulic cutting method, we can enhance the efficiency of coalbed methane development. This approach connects the natural fracture system using directional borehole and hydraulic slot, fully utilizing the permeability advantage of parallel surface cutting direction. The high-pressure hydraulic cutting process induces cracks in the coal seam, increasing the number and connectivity of diversion channels, thereby bolstering the production of coal-bed methane.

Cite this article

Leiting SHI , Qiming ZHAO , Zhenyu REN , Shijie ZHU , Shanshan ZHU . Numerical simulation study on the influence of coal rock fracture morphology on seepage capacity[J]. Petroleum Reservoir Evaluation and Development, 2023 , 13(4) : 424 -432 . DOI: 10.13809/j.cnki.cn32-1825/te.2023.04.003

References

[1] 李勇, 胡海涛, 王延斌, 等. 煤层气井低产原因及二次改造技术应用分析[J]. 矿业科学学报, 2022, 7(1): 55 -70.
[1] LI Yong, HU Haitao, WANG Yanbin, et al. Analysis of low production coalbed methane wells and application of secondary reconstruction technologies[J]. Journal of Mining Science and Technology, 2022, 7(1): 55-70.
[2] WU Y, LIU J S, ELSWORTH D. Development of anisotropic permeability during coalbed methane production[J]. Journal of Natural Gas Science and Engineering, 2010, 2(4): 197-210.
[3] WU Y, LIU J S, ELSWORTH D, et al. Dual poroelastic response of a coal seam to CO2 injection[J]. Greenhouse Gas Control, 2010, 4(4): 668-678.
[4] 罗平亚. 关于大幅度提高我国煤层气井单井产量的探讨[J]. 天然气工业, 2013, 33(6): 1-6.
[4] LUO Pingya. A discussion on how to significantly improve the single well productivity of CBM gas wells in China[J]. Natural Gas Industry, 2013, 33(6): 1-6.
[5] ROBERTSON E P, CHRISTIANSEN R L. A permeability model for coal and other fractured, sorptive-elastic media[J]. SPE Journal, 2008, 13(3): 314-324.
[6] GU F G, CHALATURNYK R. Permeability and porosity models considering anisotropy and discontinuity of coalbeds and application in coupled simulation[J]. Petroleum Science and Engineering, 2010, 74(3): 113-131.
[7] THARAROOP P, KARPYN Z T, ERTEKIN T. Development of a multi-mechanistic, dual-porosity, dual-permeability, numerical flow model for coalbed methane reservoirs[J]. Natural Gas Science and Engineering, 2012, 8: 121-131.
[8] 刘子雄. 基于微地震向量扫描的煤层气井天然裂缝监测[J]. 煤田地质与勘探, 2020, 48(5): 204-210.
[8] LIU Zixiong. Microseismic vector scanning-based natural fracture monitoring of the coalbed methane wells[J]. Coal Geology & Exploration, 2020, 48(5): 204-210.
[9] 刘世奇, 王鹤, 王冉, 等. 煤层孔隙与裂隙特征研究进展[J]. 沉积学报, 2021, 39(1): 212-230.
[9] LIU Shiqi, WANG He, WANG Ran, et al. Research progress on pore and fracture characteristics of coal seam[J]. Acta Sedimentologica Sinica, 2021, 39(1): 212-230.
[10] 李祥春, 高佳星, 张爽, 等. 基于扫描电镜、孔隙-裂隙分析系统和气体吸附的煤孔隙结构联合表征[J]. 地球科学, 2022, 47(5): 1876-1889.
[10] LI Xiangchun, GAO Jiaxing, ZHANG Shuang, et al. Combined characterization of scanning electron microscopy, pore and crack analysis system, and gas adsorption on pore structure of coal with different volatilization[J]. Earth Science, 2022, 47(5): 1876-1889.
[11] PAN Z J, CONNELL L D. Modelling permeability for coal reservoirs: A review of analytical models and testing data[J]. Coal Geology, 2012, 92(1): 1-44.
[12] XUE J H, LI Y H, LI H B, et al. Experimental study on change mechanism of coal and rock permeability under total stress and strain condition[J]. Safety in Coal Mines, 2021, 52(2): 33-37.
[13] 张雷, 郝帅, 张伟, 等. 中低煤阶煤层气储量复算及认识——以鄂尔多斯盆地东缘保德煤层气田为例[J]. 石油实验地质, 2020, 42(1): 147-155.
[13] ZHANG Lei, HAO Shuai, ZHANG Wei, et al. Recalculation and understanding of middle and low rank coalbed methane reserves: A case study of Baode Coalbed Methane Field on the eastern edge of Ordos Basin[J]. Petroleum Geology & Experiment, 2020, 42(1): 147-155.
[14] MENG Z P, ZHANG J C, WANG R. In-situ stress, pore pressure and stress-dependent permeability in the Southern Qinshui Basin[J]. International Journal of Rock Mechanics and Mining Sciences, 2011, 48(1): 122-131.
[15] WARREN J E, ROOT P J. The behavior of naturally fractured reservoirs[J]. SPE Journal, 1963, 3(3): 245-255.
[16] ELSWORTH D, MAO B. Flow-deformation response of dual-porosity media[J]. Journal of Geotechnical Engineering, 1992, 118(1): 107.
[17] 姚海鹏, 于东方, 李玲, 等. 内蒙古地区典型煤储层吸附特征[J]. 岩性油气藏, 2021, 33(2): 1-8.
[17] YAO Haipeng, YU Dongfang, LI Ling, et al. Adsorption characteristics of typical coal reservoirs in Inner Mongolia[J]. Lithologic Reservoirs, 2021, 33(2): 1-8.
[18] 石军太, 李相方, 徐兵祥, 等. 煤层气解吸扩散渗流模型研究进展[J]. 中国科学: 物理学力学天文学, 2013, 43(12): 1548-1557.
[18] SHI Juntai, LI Xiangfang, XU Bingxiang, et al. Review on desorption-diffusion-flow model of coal-bed methane[J]. Scientia Sinica Physica, Mechanica & Astronomica, 2013, 43(12): 1548-1557.
[19] 李前贵, 康毅力, 罗平亚. 煤层甲烷解吸—扩散—渗流过程的影响因素分析[J]. 煤田地质与勘探, 2003, 31(4): 26-29.
[19] LI Qiangui, KANG Yili, LUO Pingya. Analysis of the factors affecting processes of CBM desorption,diffusion and percolation[J]. Coal Geology & Exploration, 2003, 31(4): 26-29.
[20] 朱志良, 高小明. 陇东煤田侏罗系煤层气成藏主控因素与模式[J]. 岩性油气藏, 2022, 34(1): 86-94.
[20] ZHU Zhiliang, GAO Xiaoming. Main controlling factors and models of Jurassic coalbed methane accumulation in Longdong coalfield[J]. Lithologic Reservoirs, 2022, 34(1): 86-94.
[21] 刘继滨, 寇双燕, 刘继芹. 煤层气-水两相三孔介质渗流规律研究[J]. 石油化工应用, 2017, 36(10):14-19.
[21] LIU Gibin, KOU Shuangyan, LIU Jiqin. Study on coalbed methane-water two-phase seepage law in triple porosity medium[J]. Petrochemical Industry Application 2017, 36(10): 14-19.
[22] 张玉柱. 基于裂隙网络图像的煤层气流动特性研究[J]. 煤矿安全, 2021, 52(9): 172-177.
[22] ZHANG Yuzhu. Study on coalbed methane flow characteristics based on fracture network image[J]. Safety in Coal Mines, 2021, 52(9): 172-177.
[23] XIA B W, LIU S W, OU C N, et al. Experimental study on mechanical properties of sandstone with single fracture under fully-mechanized top-coal caving mining stress path[J]. Coal Science and Technology, 2022, 50(2): 95-105.
Outlines

/